C3 vented Locking Gas Cap Leaks At Vent Hole

[Jack O.]

I have what I believe is an original, or very old repop, locking gas cap on my '69. It's smooth with a rubber gasket and a vent hole that simply goes straight through from bottom to top of cap. When I fill my tank close to the neck gas comes out of that hole when driven.

Is that a known problem or is there something missing from the cap that would provide some offset or interrupt to what is now essentially a very small pipe?

Thanks,

Jack

[Joe L.]

Re: C3 vented Locking Gas Cap Leaks At Vent Hole

I have what I believe is an original, or very old repop, locking gas cap on my '69. It's smooth with a rubber gasket and a vent hole that simply goes straight through from bottom to top of cap. When I fill my tank close to the neck gas comes out of that hole when driven.

Is that a known problem or is there something missing from the cap that would provide some offset or interrupt to what is now essentially a very small pipe?

Thanks,

Jack

Jack------


This is a very well-known and notorious problem. All 1963-69 Corvette locking gas caps used a simple through-hole for ventilation, much the same arrangement as the early 1963 standard gas cap. However, even the early 63 cap was designed to be more resistant to fuel leakage than the locking gas caps.

Beginning for 1970, all Corvettes used a sealed-type gas cap and the locking gas cap had no hole for ventilation. However, both the 1963-69 and 70-74 locking caps also leak at the interface of the cap and filler neck and regardless of the condition of the gasket. That's because standard gas caps use a cam lock closing system and the locking caps use spring-loaded locking "tangs" which have never sealed well.

I absolutely do not recommend the use of a locking gas cap on any 1963-74 Corvette while it's being driven on the road. Reserve the use of the locking cap for when the car is parked in what you regard as a "threatening" situation.

[Terry M.]

Re: C3 vented Locking Gas Cap Leaks At Vent Hole

I suspect the smooth top locking gas caps are the early style and the "pebble" top are the later style.

I bought a smooth top cap the day I picked up my 1970 (last day of February 1970) and it was the smooth top style. It always leaked, both from the vent hole and the rim, if the tank was filled full up. I found the simple and effective, solution was to not fill the tank all the way up.

[Jack O.]

Re: Thanks! *** NM ***

Thanks Joe and Terry.